The invention relates to a water-conducting household appliance, especially a dishwasher having at least one essentially closed water circuit in which rinsing liquid can be circulated according to a program control unit, the rinsing liquid being conveyed through a filter element while circulating in order to filter out dirt. The invention further relates to a method for operating a water-conducting household appliance.
During the operation of a dishwasher and depending on the degree of soiling of the items being washed, large or small particles of dirt are dislodged from the items for rinsing by the rinsing liquid. In order, to prevent dirt already dislodged from the items for rinsing being transferred back onto said items by means of the rinsing liquid circulating during a particular section of the wash program, filter arrangements are arranged in the area of the washing tub or the pump well of known dishwashers. Here, a filter arrangement arranged in the pump well frequently consists of a coarse filter, which filters out from the rinsing liquid large-diameter particles of dirt, a fine filter, the mesh diameter of which lies in the range of 0.9 to 1.1 mm, and a microfilter arranged downstream of the fine filter, the mesh diameter of which is approximately 0.3 mm in order to filter out from the rinsing liquid small particles of dirt. The purpose of a filter arrangement of this kind is to filter out from the rinsing liquid as great as possible a proportion of dirt particles during circulation of said rinsing liquid. When the rinsing liquid is pumped out, for example when switching from one section of the wash program to the next, as much as possible of the dirt should be conveyed out of the washing space of the dishwasher, in order to prevent the filter arrangement from becoming clogged.
One disadvantage of the arrangement just described lies in the fact that in practice, only a portion of the dirt retained in the filter arrangement can be removed when the dishwasher is pumped out. Accordingly it is necessary that at least some of the filter elements of the filter arrangement are occasionally removed from the dishwasher by a user and manually cleaned. In order to spare said user of the dishwasher an unpleasant chore of this nature, it would be desirable if the filter arrangement were of the self-cleaning type.
A dishwasher with such a self-cleaning filter is known for example from U.S. Pat. No. 3,179,116. The filter herewith consists of a helical spring, the gaps of the spiral sections lying one above the other being variably adjustable. Upon circulation of the rinsing liquid from the washing tub to the spray arms, the spring is of lesser length and the gaps of the spiral sections thus small, so that the dirt dislodged by the rinsing liquid is filtered by the spiral spring. Upon pumping-out of the rinsing liquid, which is effected by reversing the direction of rotation of the pump, the length of the spiral spring is increased, as a result of which the distance between two adjacent spring sections increases so that dirt adhering to the spiral spring is flushed into the interior of the spiral spring, and subsequently conveyed to the water outlet. The alteration in the length of the spiral spring is effected by water pressure generated in the lines, which is dependent upon the direction of operation of a circulation pump. During the circulation, a low water pressure only is generated in a line connected to the spiral spring, by means of which the spiral spring remains of reduced length. Upon pumping out, on the other hand, high pressure is generated in the line connected to the spiral spring, by means of which the spiral spring is lengthened via a lever mechanism.
One disadvantage of the arrangement described is that the self-cleaning of the filter can only take place upon switching from one section of the wash program to the next. If, however, during one section of the wash program, the filter is subject to a large quantity of dirt, it is no longer possible for the pump to circulate sufficient rinsing liquid to soak the items being washed. The proposed arrangement thus takes into account that the cleaning effect of individual sections of the wash program may be reduced.
From DE 36 33 441 A1 an apparatus for the washing of clothing is known which has a fluff filter embodied as a disk filter and a fine filter. The fluff filter consists of wires running in parallel with each other, and is arranged in such a way that a liquid inlet aperture is located above the upper end of the wire layer and one of two liquid outlet apertures immediately behind the lower end of the wire layer. The other outlet aperture of the disk filter leads to the inlet side of the supply pump, and is located in any position in the base area of the fluff filter housing. The disk filter makes it possible during the ongoing throughput of the washing water in a number of program sections, to be able to slide fluff along the parallel wires as far as the lower end of the wire layer in front of the closable liquid outlet aperture. Upon the end of the program sections, the dirt (fluff) is then washed into the drainage system together with the outflowing washing water, by opening of the liquid outlet aperture. The fine filter serves solely to hold back detergent rinsed out of the items of clothing.
As the particles of dirt encountered during the operation of a dishwasher vary much more widely in terms of their size and properties than is the case when washing clothes, the filter described in DE 36 33 441 A1 cannot be employed in a dishwasher. In addition, as in the case of U.S. Pat. No. 3,179,116, there is the disadvantage that cleaning of the filter is only possible upon the transition from one washing program to the next.
Finally, filters for major industrial use are known from DE-OS 2 249 603 and DE-OS 29 22 549, which on account of their variable filter gaps or diameters demonstrate self-cleaning properties.